It looks to be about as strong as Web.
I think the best comparison to this spell is Web. They are both 2nd-level Wizard spells, they both cover the same area (a 20-foot cube), and they both inflict status effects on a failed save that can significantly impair an enemy's ability to fight. The main differences between them are that the area of Nathair's Mischief can move, while Web's is stationary, and that Web's effects can last for multiple rounds on a failed save, while Nathair's Mischief's effects only last for a single round.
Overall, I'd say that they're both fairly strong crowd control spells, but neither is strictly better than the other.